Anisotropic conductive adhesive sheet and connecting structure

ABSTRACT

An anisotropic conductive adhesive sheet comprising at least a curing agent, a curable insulating resin and conductive particles, wherein in a region extending from a one-side surface of the anisotropic conductive adhesive sheet along the thickness direction to a position of not greater than 2.0 times the average diameter of the conductive particles, 90% or more of the sum of conductive particles are present, the 90% or more of the sum of conductive particles being present without contact with other conductive particles, and wherein the average diameter of conductive particles is in the range of 1 to 8 μm, the average particle distance between adjacent conductive particles being in the range of 1 to 5 times the average particle diameter and not greater than 20 μm, and wherein the thickness of the anisotropic conductive adhesive sheet is at least 1.5 times the average particle distance but not greater than 40 μm.

TECHNICAL FIELD

The present invention relates to an anisotropic conductive adhesivesheet that has excellent microcircuit connecting properties, and aconnecting structure

BACKGROUND ART

Heretofore, concerning an anisotropic conductive adhesive sheet forconnecting microcircuits, various conductive particles and anisotropicconductive adhesive compositions have been examined in order to improveconnecting properties and prevent short-circuiting. For example,heretofore known methods include a method wherein insulating particleshaving a coefficient of thermal expansion equivalent are compounded toconductive particles (see Patent Document 1); a method whereininsulating particles are deposited on the surfaces of conductiveparticles in order to prevent short-circuiting (see Patent Document 2);a method wherein the surfaces of conductive particles are coated with anelectrically insulating resin (see Patent Document 3); a method whereinlayers containing and not containing conductive particles are stacked toprevent short-circuiting between adjacent circuits (see Patent Document4); a method wherein a terminal circuit is coated with a photosensitiveresin, parts other than a connecting part are selectively cured to makesuch parts not adhesive, and conductive particles are deposited on thepart having adhesion and then coated with an adhesive resin to preventshort-circuiting between adjacent circuits (see Patent Document 5); amethod wherein a peeling liner having a depression is previously formed,a single or plurality of conductive particle is disposed in thedepression, and it is deposited on an adhesive layer to fabricate ananisotropic conductive adhesive sheet (see Patent Document 6); and amethod wherein a biaxially stretchable sheet is coated with conductiveparticles, the coated sheet is stretched within a range not exceedingthe particle diameter of the conductive particles, and the isolatedconductive particles are transferred into the adhesive layer tofabricate an anisotropic conductive adhesive sheet (see Patent Document7).

However, in the conventional art wherein insulating properties areimparted to conductive particles or the like, there was limitation tomicronize the particle diameter of conductive particles for insulatingcoating or insulating coating deposition, and both the security ofinsulating properties and the security of number of connecting particlescould not be satisfied in the case of microcircuit connecting Also inthe conventional art for preventing short-circuiting by adhesivecompositions, the security of insulation properties and electricalconnecting properties were not simultaneously satisfied in the case ofmicrocircuit connecting Furthermore, in Patent Document 6, although anexample wherein a peeling liner having a depression is previously formedand a single or plurality of conductive particle is disposed in thedepression is disclosed, no examples wherein this is deposited on theadhesive layer to form an anisotropic conductive adhesive sheet aredisclosed It was actually difficult to dispose a single conductiveparticle in each depression shallower than the particle diameter of theconductive particle. To the contrary, although a single conductiveparticle could be disposed in each depression deeper than the particlediameter of the conductive particle, it was difficult to deposit on theadhesive layer As a result, the obtained anisotropic conductive adhesivecould not satisfy both the security of insulating properties and thesecurity of number of connecting particles. Also since the anisotropicconductive adhesive sheet disclosed in Patent Document 7 is based on atechnical idea to secure electrical conductivity by sandwichingconductive particles between terminals themselves and at the same timeto secure insulating properties by fixing conductive particles, theparticle diameter of conductive particles distance between adjacentconductive particles and the film thickness of the anisotropicconductive adhesive sheet must be of substantially the same values.Therefore, the gaps in the lateral direction of a terminal to be coupledwere not filled with the insulating resin, and insulation propertieswere not be satisfied. Connecting properties of terminals themselveswere also not satisfactory due to a small amount of resin. In view ofthe security of electrical conductivity, the distance between adjacentconductive particles cannot exceed the particle diameter of theconductive particles, and particularly in the case of microcircuitconnecting, it is difficult to satisfy both the security of insulatingproperties and the security of electrical connecting properties at thesame time.

Patent Document 1: JP-A-6-349339

Patent Document 2: JP Patent No. 2895872

Patent Document 3: JP Patent No. 2062735

Patent Document 4: JP-A-6-45024

Patent Document 5: JP Patent No. 3165477

Patent Document 6: JP-A-2002-519473

Patent Document 7: JP-A-2-117980

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

It is an object of the present invention to provide an anisotropicconductive adhesive sheet that realizes favorable electrical connectingproperties without impairing insulation properties between adjacentcircuits of a microcircuit, a method for the manufacture thereof and aconnecting structure using the same.

Means for Solving the Problems

As a result of extensive studies to solve the above-described problems,the present inventors have found that the problems can be solved by theuse of an anisotropic conductive adhesive sheet characterized in thatconductive particles having a certain average particle size are presentin a certain range without contact with at least a certain proportion ofconductive particles. Specifically, the present invention provides thefollowings..

(1) An anisotropic conductive adhesive sheet comprising at least acuring agent, a curable insulating resin and conductive particles,wherein 90% or more of the conductive particles are present in a regionof a thickness of not greater than 2.0 times the average particle sizeof the conductive particles extending from one surface of theanisotropic conductive adhesive sheet in the thickness direction, and90% or more of the conductive particles are present without contact withother conductive particles, wherein the average particle size of theconductive particles is 1 to 8 μm, and the average particle distancebetween adjacent conductive particles is at least once but five times orless the average particle size and not greater than 20 μm, and whereinthe thickness of the anisotropic conductive adhesive sheet is at least1.5 times the average particle distance but not greater than 40 μm.

(2) The anisotropic conductive adhesive sheet according to (1), whereinthe conductive particles are at least those selected from the groupconsisting or noble metal-coated resin particles, noble metal-coatedmetal particles, metal particles, noble metal-coated alloy particles,and alloy particles

(3) A method for manufacturing an anisotropic conductive adhesive sheetcomprising providing an adhesive layer on a biaxially stretchable filmto form a laminate, densely packing conductive particles having anaverage particle size of 1 to 8 μm on the laminate to form a conductiveparticle-attached film, biaxially stretching and holding the conductiveparticle-attached film so that the average particle distance betweenadjacent conductive particles is at least once (1) but five (5) times orless the average particle size of the conductive particles and notgreater than 20 μm, and transferring the conductive particles to anadhesive sheet containing at least a curing agent and a curableinsulating resin and having a thickness of at least 1.5 times theaverage particle distance between the conductive particles but notgreater than 40 μm.

(4) The method according to (3), wherein the biaxially stretchable filmis a long film and the adhesive sheet is a long adhesive sheet.

(5) A method for electrically connecting an electronic circuit componenthaving fine connecting terminals to a circuit board having a circuitcorresponding thereto using an anisotropic conductive adhesive sheet,comprising electrically connecting the electronic circuit component tothe circuit board having a circuit corresponding thereto using theanisotropic conductive adhesive sheet according to (1) or (2), whereinsaid electronic circuit component has a height of the fine connectingterminals of 3 to 15 times the average particle distance betweenconductive particles and not greater than 40 μm, a distance between thefine connecting terminals of 1 to 10 times the average particle distanceand not greater than 40 μm, and a pitch of the fine connecting terminalsof 3 to 30 times the average particle distance and not greater than 80μAm.

(6) A fine connecting structure obtained by the method according to (5).

Advantages of the Invention

The anisotropic conductive adhesive and connecting structure of thepresent invention have favorable insulating characteristics betweenadjacent circuits, and have favorable electrical connecting propertiesbetween coupled circuits. The present invention also exerts theabove-described effect particularly in the connecting of microcircuits

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be specifically described below

First, conductive particles in the present invention will be described.In the present invention, although heretofore known conductive particlescan be used, it is preferable to use at least those selected from thegroup consisting of noble metal-coated resin particles, noblemetal-coated metal particles, metal particles, noble metal-coated alloyparticles, and alloy particles. More preferably, these particles havemelting points not higher than 500° C. As the noble metal-coated resinparticles, the use of spherical particles of polystyrene,benzoguanamine, polymethyl methacrylate or the like coated with nickeland gold in this order is preferable. As the noble metal-coated metalparticles, the use of particles of a metal, such as nickel and copper,coated with a noble metal, such as gold, palladium and rhodium, on theoutermost layer is preferable; and as the noble metal-coated alloyparticles, the use of alloy particles described below coated with anoble metal, such as gold, palladium and rhodium, on the outermost layeris preferable. As coating methods, thin-film forming methods such asvapor deposition and sputtering, coating methods by dry blending, or wetprocesses such as electroless plating and electrolytic plating, can beused. In view of mass productivity, an electroless plating method ispreferable. As metal particles and alloy particles, the use of one ortwo or more selected from the group consisting of metals, such assilver, copper and nickel is preferable. As alloy particles, the use oflow-melting-point alloy particles having a melting point of 500° C. orbelow is preferable, and furthermore, the use of low-melting-point alloyparticles having a melting point of 350° C. or below is more preferablebecause metallic bond can be formed between connecting terminals andfrom the viewpoint of connecting reliability. When low-melting-pointalloy particles are used, it is preferable to previously coat theparticle surfaces with flux or the like. Coating with so-called flux ispreferable because oxides or the like on the surface can be removed. Asthe flux, a fatty acid or the like, such as abietic acid, can be used.

The ratio of the average particle size to the maximum particle diameterof the conductive particles is preferably 2 or less and more preferably1.5 or less. It is preferable that the particle size distribution of theconductive particles is narrower, and the geometric standard deviationof the particle size distribution of the conductive particles ispreferably 1.2 to 2.5 and more preferably 1.2 to 1.4. If the geometricstandard deviation is within the above-described values, the variationof the particle diameters is reduced. Normally, when a constant gap ispresent between two terminals to be connected, it is considered that themore even the particle diameters, the more effectively conductiveparticles function.

The geometric standard deviation of particle size distribution means thevalue obtained by dividing the σ value of the particle size distribution(the particle diameter value at 84.13% accumulation) by the particlediameter value at 50% accumulation. When particle diameters (logarithm)are set on the abscissa of the particle size distribution graph and thecumulative values (percent, cumulative number ratio, logarithm) are seton the ordinate, the particle size distribution becomes substantiallystraight line, and the particle size distribution follows logarithmicnormal distribution. The cumulative value means the ratio of the numberof particles having a certain particle diameter and smaller to the totalnumber of particles expressed in percentage The sharpness of particlesize distribution is expressed by the ratio of σ (the particle diametervalue at 84.13% accumulation) to the average particle size (the particlediameter value at 50% accumulation). The σ value is a reading value froman actual measured value or a plotted value in the above graph. Theaverage particle size and particle size distribution can be measuredusing heretofore known methods and instruments, and for themeasurements, a wet particle size distribution meter, laser particlesize distribution meter, or the like can be used. Alternatively, theparticles can be observed using an electron microscope or the like andthe average particle size and particle size distribution can becalculated. The average particle size and particle size distribution inthe present invention can be obtained using a laser particle sizedistribution meter.

The average particle size of the conductive particles is 1 to 8 μn,preferably 2 to 6 μm. In view of insulation properties, 8 μm or less ispreferable, and the effect of variation in the height of connectingterminals or the like is insignificant; and in view of electricalconnecting, 1 μm of more is preferable.

The average particle distance to adjacent conductive particles is notgreater than 20 μm and at least once to five times, preferably at least1.5 to 3 times the average particle size. In view of preventing particlecoagulation due to particle flow in connecting and securing insulationproperties, not less than once the average particle size is preferable;and in view of fine connecting, not greater than five times ispreferable.

In the present invention, adjacent conductive particles mean 6 particlesclosest to an optionally selected conductive particle. The method formeasuring the average particle distance to the adjacent conductiveparticles is as follows.

A photo enlarged by an optical microscope is taken, optional 20particles are selected, distances to 6 particles closest to eachparticle are measured, and the average value of the total is obtained tomake it the average particle distance.

The thickness of the anisotropic conductive adhesive sheet is at least1.5 times the average particle distance but not greater than 40 μm andpreferably at least twice the average particle distance but not greaterthan 40 μm. In view of mechanical connecting strength, not less than 1.5times is preferable; and in view of preventing decrease in the number ofcoupled particles due to particle flow in connecting, not greater than40 μm is preferable. The compounding quantity of conductive particles ispreferably 0.5 parts by mass to 20 parts by mass relative to 100 partsby mass, more preferably 1 part by mass to 10 parts by mass of thecomponents containing a curing agent and a curable insulating resin. Inview of insulating properties, not greater than 20 parts by mass ispreferable; and in view of electrical connecting properties, not lessthan 0.5 parts by mass is preferable.

Next, the anisotropic conductive adhesive sheet of the present inventionwill be described. In the anisotropic conductive adhesive sheet of thepresent invention, 90% or more of the conductive particles are presentin a region of a thickness of not greater than 2.0 times the averageparticle size of the conductive particles extending from one surface ofthe anisotropic conductive adhesive sheet in the thickness direction;however, it is preferable that 90% or more of them are present in aregion of 1.5 times, it is more preferable that 95% or more of them arepresent in a region of 2.0 times, and it is further preferable that 95%or more of them are present in a region of 1.5 times. Specifically, whenthe average particle size is 3.0 μm, “in a region of 2.0 times” means ina region of a thickness of 6.0 μm in the anisotropic conductivecomposition, and “90% or more of them are present in the region” meansthat 90% or more of the conductive particles are present in the layer ofthe thickness of 6.0 μm. In the anisotropic conductive adhesive sheet ofthe present invention, as the position where the conductive particlesare present to the thickness direction of the anisotropic conductiveadhesive sheet, the values of the positions of randomly selected 100conductive particles measured using a laser microscope or the like thatcan measure the displacement of the Local direction are used. At thesame time, the number of conductive particles present without contactwith other conductive particles can also be measured When thedisplacement of the focal direction is measured using the lasermicroscope, the resolution of displacement measurement is preferably 0.1μm or less, and more preferably 0.01 μm or less. As the average particlesize of the conductive particles, the value previously measuredseparately using a laser particle size distribution meter or the like isused. The thickness of the anisotropic conductive adhesive sheet of thepresent invention is preferably 3 to 20 times, more preferably 5 to 10times the average particle size of the conductive particles. From theaspect of adhesion strength of the connecting structure, not less than 3times is preferable; and from the aspect of connecting properties, lessthan 20 times is preferable. From the aspect of connecting properties,the region of not more than 2.0 times the average particle size of theconductive particles where 90% or more conductive particles are presentis preferably outside the center portion in the thickness direction ofthe conductive adhesive sheet, and more preferably, a part of theconductive particles are exposed on the surface of the anisotropicconductive adhesive sheet. The region of not greater than 2.0 times theaverage particle size of the conductive particles is preferably within½, more preferably ⅓ the thickness of the sheet in the thicknessdirection form the surface of the conductive sheet. It is alsopreferable that a part of the conductive particles are exposed on thesurface of the anisotropic conductive adhesive sheet.

Next, a method for manufacturing an anisotropic conductive adhesivesheet characterized in that conductive particles in the presentinvention are present without contact with other conductive particleswill be described. In the present invention, “conductive particles arepresent without contact with other conductive particles” means that eachof the conductive particles is present alone without coagulation.Hereafter, the expression “present alone” or “single particle” may beused for this meaning. Although known methods can be used as the methodfor manufacturing the anisotropic conductive adhesive sheet of thepresent invention, a method is preferable wherein a single layer ofconductive particles are arranged on a stretchable film or sheet, theconductive particles are dispersed and arrayed by stretching it, andthey are transferred onto an adhesive sheet composed of at least acuring agent and a curable insulating resin while maintaining thestretched state. As the stretchable film, although a known resin film orthe like can be used, the use of a homopolymer or copolymer ofpolyethylene resin, polypropylene resin, polyester resin, polyvinylalcohol resin, polyvinylbutyral resin, polyvinylidene chloride resin orthe like, or a flexible and stretchable film of a resin such as nitrylrubber, butadiene rubber, silicone rubber is preferable. Polypropyleneresin and polyester resin are particularly preferable. The shrinkingpercentage after stretching is preferably 10% or less, and morepreferably 5% or less.

As a method for dispersing, arranging and fixing conductive particles ona stretchable film, a known method can be used. For example, a methodwherein an adhesive layer containing at least a thermoplastic resin isformed on the stretchable film, conductive particles are contacted anddeposited thereon, and they are arranged in a single layer by applyingload using a rubber roll can be adopted In this case, to pack theconductive particles without gaps, repetition of deposition and rollingsteps for several times is preferable Since closest packing is the moststable structure in the case of spherical conductive particles, theconductive particles can be relatively easily packed Alternatively, amethod wherein an adhesive is applied onto the stretchable film to forman adhesive layer, conductive particles are adhered thereon, andadhesion is repeated several times, if required, to disperse and arrangethe conductive particles in a singly layer: a method wherein astretchable film is charged, the conductive particles are dispersed andadhered in a single layer and the like can be used.

Although a known methods can be used as a method for stretching astretchable film on which a single layer of conductive particles isarranged, from the aspect of even diffusing and arranging, the use ofbiaxial stretching equipment is preferable. From the aspect of distancebetween particles, the percentage of stretching is preferably 80% ormore and 400% or less, more preferably 100% or more and 300% or less.Stretching by 100% means that the length of the portion stretched alongthe stretching direction is 100% the length of the film beforestretching. Although the stretching direction is optional, biaxialstretching of a stretching angle of 90° is preferable, and simultaneousstretching is preferable. Although the stretching direction is optional,biaxial stretching of a stretching angle of 90° is preferable, andsimultaneous stretching is preferable. In the case of biaxialstretching, the percentage of stretching in each direction can be eithersame or different As the biaxial stretching equipment, simultaneousbiaxial continuous stretching equipment is preferable.

Although a known equipment can be used as the simultaneous biaxialcontinuous stretching equipment, a tenter-type stretching machinewherein long sides are fixed by chuck fittings, and the distancesbetween them are simultaneously stretched in length and width directionsto conduct continuous stretching is preferable. As the system to adjuststretching percentage, although a screw system or a pantograph systemcan be used, in view of the adjustment accuracy, the pantograph systemis more preferable. In the case of stretching while heating, it ispreferable to install a preheating zone before the stretching portion,and to install a heat fixing zone after the stretching portion.

As the method for manufacturing an anisotropic conductive adhesive sheetfrom the state wherein the conductive particles are dispersed andarranged by arranging a single layer of conductive particles on astretchable film and stretching them, the use of a method wherein apreviously fabricated adhesive sheet composed of at least a curableinsulating resin is stacked, and conductive particles or an adhesivefilm containing conductive particles is transferred, is preferable. Amethod wherein a solution containing at least an insulating resin isapplied in the dispersed and arranged state, and dried, then theanisotropic conductive adhesive sheet is peeled off the stretchablesheet or the like, can be used.

The anisotropic conductive adhesive sheet of the present invention canbe a single-layer sheet or a laminate sheet wherein an adhesive sheetnot containing conductive particles but containing at least aninsulating resin is stacked. The film thickness of the adhesive sheet tobe stacked is preferably thinner than the film thickness of the adhesivesheet containing conductive particles.

As the curable insulating resin used in the present invention, athermosetting resin, a photo-curable resin, a thermosetting andphotocurable resin, and an electron beam-curable resin can be used. Forthe ease of handling, the use of a thermosetting insulating resin ispreferable. Although epoxy resin, acrylic resin and the like can be usedas the thermosetting resin, epoxy resin is particularly preferable. Theepoxy resin is a compound having 2 or more epoxy groups in the molecule,and a compound having a glycidylether group, a glycidylester group, oran alicyclic epoxy group, and a compound wherein a double bond in themolecule is epoxidized are preferable.. Specifically, bisphenol-A-typeepoxy resin, bisphenol-F-type epoxy resin, naphthalene-type epoxy resin,novolak-phenol-type epoxy resin, or modified epoxy resin thereof can beused.

The curing agent used in the present invention can by any curing agentthat can cure the above-described thermosetting insulating resins. Whena thermosetting resin is used as the curable insulating resin, the agentthat reacts with the thermosetting resin at 100° C. or above to cure itis preferable. In the case of epoxy resin, from the aspect of storageproperties, a latent curing agent is preferable, and for example, animidazole curing agent, a capsule-type imidazole curing agent, acationic curing agent, a radical curing agent, a Lewis acid curingagent, an amine imide curing agent, a polyamine salt curing agent, ahydrazide curing agent, or the like can be used. From the aspects ofstorage properties and low-temperature reactivity, the capsule-typeimidazole curing agent is preferable.

To the anisotropic conductive adhesive sheet of the present invention,besides the curing agent and curable insulating resin, a thermoplasticresin or the like can be compounded. By compounding a thermoplasticresin, a sheet can be easily formed. The compounding quantity in thistime is preferably 200% by mass, more preferably 100% by mass of thecombined components of the curing agent and curable insulating resin.The thermoplastic resin that can be compounded in the present inventionis phenoxy resin, polyvinyl acetal resin, polyvinyl butyral resin,alkylated cellulose resin, polyester resin, acrylic resin, styreneresin, urethane resin, polyethylene terephthalate resin, and the like.Such resins can be selectively used alone or in a combination of two ormore. Among these resins, a resin having a polar group, such as hydroxyland carboxyl groups, is preferable from the aspect of adhesive strength.Furthermore, it is preferable that the thermoplastic resin contains oneor more thermoplastic resin having a glass transition temperature of 80°C. or above.

In the anisotropic conductive adhesive sheet of the present invention,additives can be compounded to the above-described components In orderto improve the adhesion between the anisotropic conductive adhesivesheet and the deposited material, a connecting agent can be compoundedas an additive. As the connecting agent, although a silane connectingagent, titanium connecting agent, or aluminum connecting agent can beused, the silane connecting agent is preferable. As the silaneconnecting agent, γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropyltriethoxysilane, γ-mercaptotrimethoxysilane,γ-aminopropyltrimethoxysilane,β-aminoethyl-γ-aminopropyltrimethoxysilane,γ-ureidopropyltrimethoxysilane, or the like can be used. The compoundingquantity of the connecting agent is preferably 0.01 part by mass to 1part by mass based on 100 parts by mass of the combination of the curingagent and curable insulating resin. In view of improving adhesion, 0.01part by mass or more is preferable and in view of reliability, 1 part bymass or less is preferable.

Furthermore, in order to prevent the lowering of insulating propertiesdue to ionic components in the anisotropic conductive adhesive sheetwhen absorbing moisture, an ion scavenger can be compounded as anadditive. As the ion scavenger, although an organic ion exchanger, aninorganic ion exchanger, an inorganic ion adsorbing agent, or the likecan be used, an inorganic ion exchanger, which has excellent heatresistance, is preferable As the inorganic ion exchanger, a zirconiumcompound, a zirconium-bismuth compound, an antimony-bismuth compound, amagnesium-aluminum compound, or the like can be used. Although the typesof ions to be exchanged include a cation type, an anion type, and anamphoteric ion type, the amphoteric ion type is preferable because itcan exchange both metal ions (cations), which directly cause ionmigration, and anions, which cause the elevation of electricalconductivity and the formation of metal ions. The average particle sizeof the ion scavenger to be compounded is preferably 0.01 μm or more and5 μm or less, more preferably 0.01 μm or more and 1 μm or less.

Next, a method for manufacturing the anisotropic conductive adhesivesheet of the present invention will be described.

First, an adhesive layer is provided on a biaxially stretchable film toform a laminate, conductive particles having an average particle size of1 to 8 μm are closely packed on the laminate to fabricate aconductive-particle adhered film, the conductive-particle adhered filmis biaxially stretched and held so that the average particle distancebetween the conductive particles and adjacent particles is at least oncebut five times or less the average particle size of the conductiveparticles and 20 μm or less, and the conductive particles aretransferred on an adhesive sheet containing at least a curing agent anda curable insulating resin and having a thickness of 1.5 times or morethe average particle distance of the conductive particles and 40 μm orless, to manufacture the anisotropic conductive adhesive sheet of thepresent invention Preferably, the biaxially stretchable film is a longfilm, and the adhesive sheet is also a long adhesive sheet.

Although known adhesives can be used in the adhesive layer, when biaxialstretching is performed while heating, the use of a non-thermalcross-linking adhesive is preferable. Specifically, a natural rubberlatex adhesive, a synthetic rubber latex adhesive, a synthetic resinemulsion adhesive, silicone adhesive, ethylene-vinyl acetate copolymeradhesive, and the like can be used alone or in combination. As theadhesion of the adhesive, the peeling strength of the surface of thesurface metal of the conductive particles to be used is preferablywithin a range between 0.5 gf/cm and 40 gf/cm, more preferably within arange between 1 gf/cm and 20 gf/cm. As the measuring method, a methodwherein a glass plate coated with a metal having the same composition asthe surface metal of the conductive particles is prepared, a film havinga width of 2 cm coated with the adhesive is adhered, and 90° peelingstrength is measured, can be used. In view of holding the conductiveparticles when the conductive particles are adhered and when the film isstretched, the peeling strength is preferably 0.5 gf/cm or more; and inview of transferring particles to the adhesive sheet after stretching,the peeling strength is preferably 40 gf/cm or less. The thickness ofthe adhesive layer is preferably within a range between 1/50 and twice,more preferably 1/10 and once the average particle size of theconductive particles to be used. In view of holding the conductiveparticles when the conductive particles are adhered and when the film isstretched, the thickness is preferably 1/50 or more the average particlesize of the conductive particles; and in view of transferring particlesto the adhesive sheet after stretching, the thickness is preferablytwice or less. As the method for forming the adhesive layer, a methodwherein the adhesive dispersed or dissolved in a solvent or water isapplied using a heretofore known method, such as a gravure coater, diecoater, knife coater, bar coater, or the like, and dried, can be used.When a hot-melt-type adhesive is applied, roll coating without solventcan be performed.

As the method for closely packing the conductive particles, theabove-described method wherein conductive particles are dispersed andarranged on a stretchable film and fixed can be used.

The film thickness of the film after stretching is preferably 1/10 toonce, more preferably ⅕ to ½ of the sum of the film thickness of theadhesive sheet to be transferred and the support film of the adhesivesheet. In view of handling the film after stretching, the film thicknessis preferably 1/10 or more of the sum of the film thickness; and in viewof transferring particles to the adhesive sheet after stretching, thefilm thickness is preferably once or less of the sum of the filmthickness.

The present invention also relates to a method for electricallyconnecting an electronic circuit component having fine connectingterminals to a circuit board having a circuit corresponding to theelectronic circuit component using an anisotropic conductive adhesivesheet. In the fine connecting method, the height of the fine connectingterminal of the electronic circuit component is 3 to 15 times theaverage particle distance of the conductive particles but not greaterthan 40 μm, the distance between the fine connecting terminals is 1 to10 times the average particle distance but not greater than 40 μm, andthe pitch of the fine connecting terminals is 3 to 30 times the averageparticle distance of the conductive particles but not greater than 80μm. The electronic circuit component is electrically coupled to thecircuit board having a circuit corresponding to the electronic circuitcomponent using the anisotropic conductive adhesive sheet of the presentinvention.

The height of the connecting terminal is 3 to 15 times the averageparticle distance of the conductive particles but not greater than 40μm, and 4 to 10 times are preferable. In view of the mechanical strengthof the connecting structure, not less than 3 times are preferable; andin view of the movement of conductive particles due to the resin flow ofthe adhesive sheet occurring in connecting, the lowering of connectingproperties due to lowered number of conductive particles in the lowerportion of the connecting terminal, the movement of conductive particlespresent in the area other than the connecting portion, and the loweringof insulating properties due to coagulation, not more than 15 times andnot more than 40 μm are preferable. The distance between connectingterminals is once to 10 times the average particle distance but notgreater than 40 μm, preferably once to 10 times but not greater than 20μm, and more preferably 2 to 5 times but not greater than 15 μm. In viewof insulating properties, once or more is preferable and in view of fineconnecting, not more than 10 times and not greater than 40 μm ispreferable. The pitch is 3 to 30 times the average particle distance butnot greater than 80 μm, and preferably 5 to 20 times but not greaterthan 40 μm. In view of connecting properties, 3 times or more ispreferable; and in view of fine connecting, not more than 30 times butnot greater than 80 μm is preferable.

The present invention also relates to a fine connecting structureconnected by the above-described fine connecting method.

The material of the circuit bard coupled using an anisotropic conductiveadhesive sheet of the present invention can be either an organic boardor an inorganic board. As the organic board, a polyimide film board, apolyamide film board, a polyethersulfone film board, a rigid boardproduced by impregnating epoxy resin into glass cloth, a rigid boardproduced by impregnating bismaleimide-triazine resin into glass cloth,or the like can be used. As the inorganic board, a silicon board, aglass board, an alumina board, an aluminum nitride board, or the likecan be used. As the wiring material for a wiring board, an inorganicwiring material, such as indium tin oxide, indium zinc oxide or thelike; a metal wiring material, such as gold-plated copper,chromium-copper, aluminum and gold bumps; a composite wiring materialwherein an inorganic wiring material such as indium tin oxide is coveredwith a metallic material, such as aluminum and chromium, or the like canbe used.

The distance between connecting circuits used in the present inventionis preferably 3 to 500 times the average particle size of conductiveparticles in view of electrical insulating properties. In the connectingcircuit used in the present invention, the connecting area of thecircuit portion to be connected is preferably 1 to 10000 times thesquare of the value of the above-described average particle size. Fromthe aspect of connecting properties, 2 to 100 times are particularlypreferable

The anisotropic conductive adhesive sheet of the present invention orthe connecting structure of the present invention can be used forconnecting the display device, such as a liquid crystal display device,a plasma display device, and an electroluminescence display device to awiring board; mounting electronic parts, such as an LSI, of thesedevices; connecting other devices to a wiring board; and mountingelectronic parts, such as an LSI. Among the above-described displaydevices, the anisotropic conductive adhesive sheet or the connectingstructure can be suitably used in the plasma display device, and theelectroluminescence display device, which require reliability.

Next, the present invention will be described in further detailreferring to examples and comparative examples.

EXAMPLE 1

In an ethyl acetate-toluene mixed solvent (mixing ratio of 1:1), 37 g ofa phenoxy resin (glass transition temperature: 98° C., number averagemolecular weight: 14000), 26 g of a bisphenol-A-type epoxy resin (epoxyequivalent: 190, viscosity at 25° C.: 14000 mPaS), and 0.3 g ofγ-glycidoxypropyltrimethoxysilane were dissolved to produce a solutionhaving a solid content of 50%.

In the solution having a solid content of 50%, 37 g of a liquid epoxyresin containing a microcapsule-type latent imidazole curing agent(average particle size of the microcapsules: 5 μm, activatingtemperature: 125° C.) was compounded and dispersed Thereafter, thedispersion was applied onto a polyethylene terephthalate film having athickness of 50 μm, wind-dried at 60° C. for 15 minutes to obtain afilm-like adhesive sheet having a film thickness of 20 μm.

Onto a non-stretched polypropylene film having a thickness of 45 μmcoated with a nitrile rubber latex-methyl methacrylate graft copolymeradhesive having a thickness of 5 μm, a single layer of gold-platedplastic particles of an average particle size of 3.0 μm were applied soas to be substantially free of gaps. Specifically, a container having awidth larger than the width of the film packed with the gold-platedplastic particles so as to have a thickness of several layers wasprepared, the film with the adhesive applied surface facing downward waspressed against the gold-plated particles to adhere, and thereafter,excessive particles were scraped down with a scraper made of a non-wovenfabric. By repeating this procedure twice, a single-layer coated filmwithout gaps was obtained. The particle size distribution of thegold-plated plastic particles was previously measured using a laserparticle size distribution meter (HELOS SYSTEM, manufactured by JEOL),and the value at 50% cumulative value was made to be the averageparticle size. The film was fixed using a biaxial stretching equipment(corner stretching type biaxial stretching equipment of pantographsystem, X6H-S manufactured by Toyo Seiki Seisaku-sho, Ltd.) using 10chucks in each of lengthwise and crosswise directions, preheated at 150°C. for 120 seconds, then, stretched by 100% in each of lengthwise andcrosswise directions at a rate of 20%/sec and fixed. After stacking theadhesive sheet on the stretched film, the adhesive sheet was peeled offto obtain an anisotropic conductive adhesive sheet. From the conductiveparticles on the obtained anisotropic conductive adhesive sheet, 100particles were randomly selected, and the distance from the surface ofthe anisotropic conductive adhesive sheet was measured using a lasermicroscope that can measure the displacement in the Local pointdirection (VK9500, manufactured by Keyence Corporation, shapemeasurement resolution: 0.01 μm). As a result, it was known that 95% ofthe conductive particles were present within the layer shown in a rangeof 5.5 μm in the film thickness direction of the anisotropic conductiveadhesive sheet. Of the 100 measured conductive particles, 92% weresingle particles. The average distance between particles was 4.17 μm,which was 1.39 times the average particle size.

EXAMPLE 2

In an ethyl acetate-toluene mixed solvent (mixing ratio: 1:1), 42 g of aphenoxy resin (glass transition temperature: 45° C., number averagemolecular weight: 12000), 32 g of a naphthalene-type epoxy resin (epoxyequivalent: 136, semisolid), and 0.06 g ofγ-ureidopropyltrimethoxysilane were dissolved to produce a solutionhaving a solid content of 50%. In the solution having a solid content of50%, 26 g of a liquid epoxy resin containing a microcapsule-type latentimidazole curing agent (average particle size of the microcapsules: 5μm, activating temperature: 125° C.) was compounded and dispersed.Thereafter, the dispersion was applied onto a polyethylene terephthalatefilm having a thickness of 50 μm, wind-dried at 60° C. for 15 minutes toobtain a film-like adhesive sheet having a film thickness of 15 μm.

Onto a non-stretched polypropylene film having a thickness of 45 μmcoated with a nitrile rubber latex-methyl methacrylate graft copolymeradhesive having a thickness of 5 μm, a single layer of gold-platedplastic particles of an average particle size of 2.5 μm were applied inthe same manner as in Example 1 so as to be substantially free of gaps.The film was stretched using biaxial stretching equipment by 120% ineach of lengthwise and crosswise directions in the same manner as inExample 1, and fixed. After stacking the adhesive sheet on the stretchedfilm, the adhesive sheet was peeled off to obtain an anisotropicconductive adhesive sheet From the conductive particles on the obtainedanisotropic conductive adhesive sheet, 100 particles were randomlyselected, and the distance from the surface of the anisotropicconductive adhesive sheet was measured using a laser displacement gage.As a result, it was known that 95% of the conductive particles werepresent within the layer shown in a range of 4.8 μm in the filmthickness direction of the anisotropic conductive adhesive sheet of the100 measured conductive particles, 91% were single particles. Theaverage distance between particles was 4.24 μm, which was 1.70 times theaverage particle size.

EXAMPLE 3

In an ethyl acetate-toluene mixed solvent (mixing ratio: 1:1), 15 g of aphenoxy resin (glass transition temperature: 45° C., number averagemolecular weight: 12000), 24 g of a phenoxy resin (glass transitiontemperature: 98° C., number average molecular weight: 14000), 26 g of anaphthalene-type epoxy resin (epoxy equivalent of 136, semisolid), and0.1 g of γ-glycidoxypropyltrimethoxysilane were dissolved to produce asolution having a solid content of 50%. In the solution having a solidcontent of 50%, 35 g of a liquid epoxy resin containing amicrocapsule-type latent imidazole curing agent (average particle sizeof the microcapsules: 5 μm, activating temperature: 125° C.) wascompounded and dispersed. Thereafter, the dispersion was applied onto apolyethylene terephthalate film having a thickness of 50 μm, wind-driedat 60° C. for 15 minutes to obtain a film-like adhesive sheet A having afilm thickness of 15 μm.

Furthermore, a film-like adhesive sheet B having a film thickness of 5μm was obtained in the same manner as described except that apolyethylene terephthalate film undergone easy-peeling treatment wasused.

Onto a non-stretched polypropylene film having a thickness of 45 μmcoated with a nitrile rubber latex-methyl methacrylate graft copolymeradhesive having a thickness of 5 μm, a single layer of gold-platednickel particles of an average particle size of 2.6 μm were applied inthe same manner as in Example 1 so as to be substantially free of gaps.The film was stretched using biaxial stretching equipment by 200% ineach of lengthwise and crosswise directions in the same manner as inExample 1, and fixed. After stacking the adhesive sheet A on thestretched film, the adhesive sheet was peeled off, and the adhesivesheet B was stacked on the peeled surface to obtain an anisotropicconductive adhesive sheet From the conductive particles on the obtainedanisotropic conductive adhesive sheet, 100 particles were randomlyselected, and the distance from the surface of the anisotropicconductive adhesive sheet was measured using a laser displacement gage.As a result, it was known that 95% of the conductive particles werepresent within the layer shown in a range of 4.9 μm in the filmthickness direction of the anisotropic conductive adhesive sheet. Of the100 measured conductive particles, 91% were single particles. Theaverage distance between particles was 7.22 μm, which was 2.77 times theaverage particle size.

COMPARATIVE EXAMPLE 1

In an ethyl acetate-toluene mixed solvent (mixing ratio of 1:1), 37 g ofa phenoxy resin (glass transition temperature: 98° C., number averagemolecular weight: 14000), 26 g of a bisphenol-A-type epoxy resin (epoxyequivalent: 190, viscosity at 25° C.: 14000 mPaS), and 0.3 g ofγ-glycidoxypropyltrimethoxysilane were dissolved to produce a solutionhaving a solid content of 50%.

In the solution having a solid content of 50%, 37 g of a liquid epoxyresin containing a microcapsule-type latent imidazole curing agent(average particle size of the microcapsules: 5 μm, activatingtemperature: 125° C,), and 2. 0 g of gold-plated plastic particleshaving an average particle size of 3.0 μm was compounded and dispersed.Thereafter, the dispersion was applied onto a polyethylene terephthalatefilm having a thickness of 50 μm, wind-dried at 60° C. for 15 minutes toobtain a film-like anisotropic adhesive sheet having a film thickness of20 μm.

From the conductive particles on the obtained anisotropic conductiveadhesive sheet, 100 particles were randomly selected, and the distancefrom the surface of the anisotropic conductive adhesive sheet wasmeasured using a laser displacement gage. As a result, it was known thatconductive particles were randomly present in the film thicknessdirection of the anisotropic conductive adhesive sheet. Of the 100measured conductive particles, 75% were single particles.

COMPARATIVE EXAMPLE 2

In an ethyl acetate-toluene mixed solvent (mixing ratio of 1:1), 42 g ofa phenoxy resin (glass transition temperature: 45° C., number averagemolecular weight: 12000), 32 g of a naphthalene-type epoxy resin (epoxyequivalent of 136, semi-solid), and 0.06 g ofγ-ureidopropyltrimethoxysilane were dissolved to produce a solutionhaving a solid content of 50%. In the solution having a solid content of50%, 26 g of a liquid epoxy resin containing a microcapsule-type latentimidazole curing agent (average particle size of the microcapsules: 5μm, activating temperature: 125° C.), and 6.0 g of gold-plated nickelparticles having an average particle size of 2.6 μm was compounded anddispersed. Thereafter, the dispersion was applied onto a polyethyleneterephthalate film having a thickness of 50 μm, wind-dried at 60° C. for15 minutes to obtain a film-like anisotropic adhesive sheet having afilm thickness of 20 μm.

From the conductive particles on the obtained anisotropic conductiveadhesive sheet, 100 particles were randomly selected, and the distancefrom the surface of the anisotropic conductive adhesive sheet wasmeasured using a laser displacement gage. As a result, it was known thatconductive particles were randomly present in the film thicknessdirection of the anisotropic conductive adhesive sheet. Of the 100measured conductive particles, 70% were single particles.

COMPARATIVE EXAMPLE 3

As anisotropic conductive adhesive sheet was obtained in the same manneras in Example 1 except that gold-plated plastic particles of an averageparticle size of 10 μm were used, and the sheet was stretched by 60%.From the conductive particles on the obtained anisotropic conductiveadhesive sheet, 100 particles were randomly selected, and the distancefrom the surface of the anisotropic conductive adhesive sheet wasmeasured using a laser displacement gage. As a result, it was known that96% of the conductive particles were present within the layer shown in arange of 19.2 μm in the film thickness direction of the anisotropicconductive adhesive sheet.

Of the 100 measured conductive particles, 93% were single particles. Theaverage distance between particles was 852 μm, which was 0.85 times theaverage particle size.

(Method for Measuring Connecting Resistance Value)

After forming an oxide film on the entire surface of a silicon piece(thickness: 0.5 mm) having a width of 1.6 mm and a length of 15.1 mm,175 and 16 thin aluminum films (1000 angstroms) each having a width of74.5 μm and a length of 120 μm were formed on the long side and theshort side, respectively, 40 μm inside of the peripheral portions, sothat the each distance between films becomes 0.1 μm. In order to formtwo gold bumps (thickness: 15 μm) each having a width of 25 μm and alength of 100 μm on each of these thin aluminum films so as to have adistance of 15 μm, on the portion other than an opening having a widthof 10 μm and a length of 85 μm on 7.5 μm inside of the peripheralportion of the gold-bump disposing position, a polyimide protective filmwas formed on the entire surface other than the above-described openingusing a normal method. Thereafter, the above-described gold bumps wereformed to be test chips.

On alkali-free glass of a thickness of 0.7 mm, a connecting pad (width:66 μm, length: 120 μm) of indium-tin oxide (thickness: 1400 angstrom)was formed so as to be connected in the position relationship to be apair with a gold bump on the thin aluminum film adjacent to a gold bumpon the above-described thin aluminum film. Each time 20 gold bumps wereconnected, an outgoing wiring of a thin indium-tin oxide was formed onthe above-described connecting pad, and a thin aluminum-titanium film(titanium: 1%, 3000 angstroms) was formed on the outgoing wiring to be aconnecting evaluating board. On the above-described connectingevaluating board, an anisotropic conductive adhesive sheet having awidth of 2 mm and a length of 17 mm was temporarily bonded so that theentire connecting pad was covered, and after pressing at 80° C. under0.3 MPa for 3 seconds using a pressure bonding head of a width of 2.5mm, the base film of polyethylene terephthalate was Peeled off. A testchip was placed thereon so that the locations of the above-describedconnecting pad and gold bump are aligned and pressure-bonded at 220° C.for 5 seconds under 5.2 MPa. After pressure bonding, the resistancevalue between the above-described outgoing wirings (daisy chain of 20gold bumps) was measured using a resistance meter of a 4-terminal methodto be a connecting resistance value.

(Method for Testing Insulation Resistance)

On alkali-free glass of a thickness of 0.7 mm, a connecting pad (width:65 μm, length: 120 μm) of indium-tin oxide (1400 angstrom) was formed inthe position relationship so that 2 gold bumps on the above-describedthin aluminum film could be coupled to each other. A connecting wiringof a thin indium-tin oxide was formed so that 5 connecting pads could bealternately coupled, and another connecting wiring of a thin indium-tinoxide was formed so that 5 connecting pads could be alternately coupledso as to be pair with them and form a comb-shaped pattern. On eachconnecting wiring, an outgoing wiring of a thin indium-tin oxide filmwas formed, and a thin aluminum-titanium film (titanium: 1%, 3000angstroms) was formed on the outgoing wiring to be an insulatingproperty evaluating board. On the above-described insulating propertyevaluating board, an anisotropic conductive adhesive sheet having awidth of 2 mm and a length of 17 mm was temporarily bonded so that theentire connecting pad was covered, and after pressing at 80° C. under0.3 MPa for 3 seconds using a pressure bonding head of a width of 2.5mm, the base film of polyethylene terephthalate was peeled off. A testchip was placed thereon so that the locations of the above-describedconnecting pad and gold bump are aligned and pressure-bonded at 220° C.for 5 seconds under 2.6 MPa to be an insulating resistance testing board

While holding the insulating resistance testing board at 60° C. and arelative humidity of 90%, a DC voltage of 100 V was impressed betweenpaired outgoing wirings using a constant-voltage constant-current powersource. The insulation resistance between these wirings was measuredonce every 5 minutes, and time until the insulation resistance valuebecomes 10 MΩ or less was measured to be an insulation lowering time.The case when the insulation lowering time was less than 240 hours wasevaluated as×(bad), and the case of 240 hours or more was evaluated as ◯(good);.

The above results are shown in Table 1. TABLE 1 Connection resistancevalue Insulation (Ω) resistance test Example 1 12.4 ◯ (good) Example 211.9 ◯ (good) Example 3 13.5 ◯ (good) Comparative 26.2 X (bad) Example 1(short-circuiting) Comparative 14.0 X (bad) Example 2 (short-circuiting,initial) Comparative 13.1 X (bad) Example 3 (short-circuiting, initial)

As is obvious from Table 1, the anisotropic conductive adhesiveaccording to the present invention exerts very excellent insulationreliability.

INDUSTRIAL APPLICABILITY

The anisotropic conductive adhesive sheet according to the presentinvention exerts low connecting resistance and high insulationreliability, and is suitable as a bare chip connecting material whereinfine circuit connecting is required, and a connecting material for ahigh-definition display device and the like.

1. An isotropic conductive adhesive sheet comprising at least a curingagent, a curable insulating resin and conductive particles, wherein 90%or more of the conductive particles are present in a region of athickness of not greater than 1.5 times the average particle size of theconductive particles extending from one surface of the anisotropicconductive adhesive sheet in the thickness direction, and 90% or more ofthe conductive particles are present without contact with otherconductive particles, wherein the average particle size of theconductive particles is 1 to 8 μm, and the average particle distancebetween adjacent conductive particles is at least once but five times orless the average particle size and not greater than 20 μm, and whereinthe thickness of the anisotropic conductive adhesive sheet is at least1.5 times the average particle distance but not greater than 40 μm. 2.The anisotropic conductive adhesive sheet according to claim 1, whereinthe conductive particles are at least those selected from the groupconsisting of noble metal-coated resin particles, noble metal-coatedmetal particles, metal particles, noble metal-coated alloy particles,and alloy particles.
 3. A method for manufacturing an anisotropicconductive adhesive sheet comprising providing an adhesive layer on abiaxially stretchable film to form a laminate, densely packingconductive particles having an average particle size of 1 to 8 μm on thelaminate to form a conductive particle-attached film, biaxiallystretching and holding the conductive particle-attached film so that theaverage particle distance between adjacent conductive particles is atleast once but five times or less the average particle size of theconductive particles and not greater than 20 μm, and transferring theconductive particles to an adhesive sheet containing at least a curingagent and a curable insulating resin and having a thickness of at least1.5 times the average particle distance between the conductive particlesbut not greater than 40 μm.
 4. The method according to claim 3, whereinthe biaxially stretchable film is a long film and the adhesive sheet isa long adhesive sheet.
 5. A method for electrically connecting anelectronic circuit component having fine connecting terminals to acircuit board having a circuit corresponding thereto using ananisotropic conductive adhesive sheet, comprising electricallyconnecting the electronic circuit component to the circuit board havinga circuit corresponding thereto using the anisotropic conductiveadhesive sheet according to claim 1, wherein said electronic circuitcomponent has a height of the fine connecting terminals of 3 to 15 timesthe average particle distance between conductive particles and notgreater than 40 μm, a distance between the fine connecting terminals of1 to 10 times the average particle distance and not greater than 40 μm,and a pitch of the fine connecting terminals of 3 to 30 times theaverage particle distance and not greater than 80 μm.
 6. A fineconnecting structure obtained by the method according to claim
 5. 7. Ananisotropic conductive adhesive sheet comprising at least a curingagent, a curable insulating resin and conductive particles manufacturedby the method according to claim 3, wherein 90% or more of theconductive particles are present in a region of a thickness of notgreater than 1.5 times the average particle size of the conductiveparticles extending from one surface of the anisotropic conductiveadhesive sheet in the thickness direction, and 90% or more of theconductive particles are present without contact with other conductiveparticles, wherein the average particle size of the conductive particlesis 1 to 8 μm, and the average particle distance between adjacentconductive particles is at least once but five times or less the averageparticle size and not greater than 20 μm, and wherein the thickness ofthe anisotropic conductive adhesive sheet is at least twice the averageparticle distance but not greater than 40
 8. A method for electricallyconnecting an electronic circuit component having fine connectingterminals to a circuit board having a circuit corresponding theretousing an anisotropic conductive adhesive sheet, comprising electricallyconnecting the electronic circuit component to the circuit board havinga circuit corresponding thereto using the anisotropic conductiveadhesive sheet according to claim 2, wherein said electronic circuitcomponent has a height of the fine connecting terminals of 3 to 15 timesthe average particle distance between conductive particles and notgreater than 40 μm, a distance between the fine connecting terminals of1 to 10 times the average particle distance and not greater than 40 μmand a pitch of the fine connecting terminals of 3 to 30 times theaverage particle distance and not greater than 80 μm.